MICROFLEX Project: MEMS on New Emerging Smart Textiles/Flexibles

MICROFLEX Project: MEMS on New Emerging Smart Textiles/Flexibles S Beeby, M J Tudor, R Torah, K Yang, Y Wei Dr Steve Beeby ESD Research Group Smart Fabrics 2011 5 th April 2011

Overview Introduce the MicroFlex project What are MEMS? How are they made MicroFlex developments Case Study: Printed strain gauge on fabric Case Study 2: Printed piezoelectrics on fabrics 2

Research at Southampton ECS was founded over 60 years ago 106 academic staff (36 professors) 140 research fellows, 250 PhD students Research grant income: over 12 million Over 20 years experience in developing printable active materials 4 research projects on smart fabrics: Microflex (EU Integrated Project) Bravehealth (EU Integrated Project) Energy Harvesting Materials for Smart Fabrics and Interactive Textiles (EPSRC) Intelligent prosthetics (UK MOD) 100 million Mountbatten Building, housing state of the art cleanroom. 3

MicroFlex Project The MicroFlex Project is a EU FP 7 funded integrated project, 7.7 M Budget, 5.4 M funding. 4 Year project, end date 30 th October 2012. 13 Partners, 7 industrial, 9 countries. Develop MEMS processing capability for the production of flexible smart fabrics. Based on screen and inkjet printing. Develop new functional inks to be compatible with fabrics. Produce industrial prototypes demonstrating the functionality of the new inks. http://microflex.ecs.soton.ac.uk 4

Envisaged Process Flow Active material Functional inks Lab trials Design & simulation Screen printing Curing Ink jet printing MEMs on fabric Fabric Sacrificial layer removal process 5

Example Functions and Applications Drug delivery Medical Smart bandage, auto sterilization uniform, active monitoring underwear Mechanical action Transport Luminous cabin, smart driver seat, auto clean filters Lighting Sensor Workwear Consumer Danger warning workwear (heating suite, high visibility, gas sensing, temperature sensing, movement sensing, alarm sounder Massage and cooling/heating armchair, surroundings customisation 6

Example Functions and Applications Drug delivery Medical Smart bandage, auto sterilization uniform, active monitoring underwear Mechanical action Transport Luminous cabin, smart driver seat, auto clean filters Lighting Sensor Workwear Consumer Danger warning workwear (heating suite, high visibility, gas sensing, temperature sensing, movement sensing, alarm sounder Massage and cooling/heating armchair, surroundings customisation 7

MEMS The MicroFlex project is concentrating on fabricating sensors and actuators (transducers). MEMS stands for MicroElectroMechanical Systems, i.e. they are systems that include mechanical and electrical functionality. Typical MEMS are miniature sensors and actuators. MEMS technology is dominated by Silicon microfabrication technology, although polymer materials / processes becoming increasingly used. 8

Example MEMS Analogue devices ADXL 50 2 axis accelerometer, 3 mm 2 surface area for integrated electronics and mechanical sensing element y x Mechanical element Inertial mass displacements sensed by interdigital electrode array. 9

Example MEMS 2 Texas Instruments Digital Light Processors (DLP) 2 million mirrors, 13μm wide http://www.dlp.com 10

MEMS Fabrication Poly Si Silicon Silicon Nitride Dry etch Silicon Dioxide Dry etch Wet etch 11

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MEMS Fabrication on Fabrics Fabrics present a very different substrate compared with a silicon wafer Rough, uneven surface with pilosity Flexible and elastic Suitable for low temperature processing Limited compatibility with solvents and chemicals MicroFlex aims to use standard printing techniques to deposit a range of custom inks in order to realise freestanding mechanical structures coupled with active films for sensing and actuating. 13

Screen Printing Also known as thick-film printing, this is normally used in the fabrication of hybridised circuits and in the manufacture of semiconductor packages. ink Mesh Mask a) b) Substrate Squeegee Substrate c) d) Substrate Substrate 14

Inkjet Printing Non contact direct printing onto substrate, used for fabrics and electronics applications. http://spie.org/x18497.xml?articleid=x18497 15

Printed MEMS Process Electrode Piezoresistive layer Structural layer Sacrificial layer Fabric Interface layer Sacrificial layer requirements: printable, solid, compatible, can be easily removed without damaging fabric or other layers. Structural layer requirements: suitable mechanical/functional properties. 16

Case Study: Strain Gauge The MicroFlex project is structured so as to initially demonstrate the functional inks, and then use these in the sacrificial layer process. Printed strain gauge demonstrated by project partners Jožef Stefan Institute, ink developed by ITCF and fabric from Saati. Exploits the piezoresistive effect: the resistance of a printed film changes as it is strained (stretched) due to a change in the resistivity of the material. Useful for sensing movement, forces and strains. 17

Printed Sensor Silver electrodes printed using a low temperature polymer silver paste. Piezoresisive paste is based on graphite. Cured at 120-125 o C 1 print 2 prints 3 prints 18

Results Sensitivity illustrated by the Gauge factor: GF ΔR R = ε Clear increase in resistance demonstrated as the fabric is strained. N of graphite R 0 (Ω) at 0 % R(Ω) at 1.5 % Gauge factor layer strain strain 1 1905 2064 5.6 2 1100 1198 5.9 3 328 358 6.1 Conventional metal foil GF = 2 19

Strain vs Load By measuring resistance the load on the fabric can be calculated. Load (N) 25 20 15 10 5 warp 1 layer 2 layers 3 layers 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Strain (%) B. Perc, et al. Thick-film strain sensor on textiles, 45th International Conference on Microelectronics, Devices and Materials - MIDEM, Slovenia 9-11 Sept 2009. 20

Piezoelectric Films Piezoelectric materials expand when subject to an electrical field, similarly they produce an electrical charge when strained. http://www.piezomaterials.com Ideal material for sensing and actuating applications. Meggitt have developed a screen printable piezoelectric paste that can be printed onto fabrics. 21

Piezoelectric Structure Piezoelectric material sandwiched between electrodes. Polarising voltage required after printing to make the piezoelectric active. Cured at temperatures below 150 o C. Promising sensitivity demonstrated (d 33 ~ 30 pc/n) Images courtesy of Meggitt Sensing Systems 22

Other Examples Screen and inkjet printed conductors on fabric. Evaluating conduction and flexibility. Screen printed heater on fabric. Evaluating heating effects on fabric. Screen printed electro-luminescent lamp on fabric. Evaluating lamp performance and compatibility with fabric. 23

Conclusions MEMS technology is widely established in a multitude of applications. MicroFlex will develop the materials and processes required to fabricate MEMS on fabrics. Range of active inks has already been demonstrated. Currently preparing phase one prototypes based upon these active inks. Sacrificial layer fabrication process has also been demonstrated and will be combined with active inks in phase two prototypes. 24

Acknowledgements Colleagues at Southampton, MicroFlex partners and EU for funding (CP-IP 211335-2). Thanks for your attention! 25